The present invention relates to a tool intended to be rotatably mounted in a road planing cutter. The tool in its operative position carries out snow clearing and scraping of especially tough/hard ice and of other tough/hard road surface. The longitudinal axis of the tool forms an angle with the road surface in the interval of 20.degree.-90.degree. and a metal tip or a hard metal tip of the tool contacts the road surface in the operative position of the tool. The invention also relates to the metal tip per se and a method to work road surfaces.
The conventional road-grading steels have during the years been improved step by step due to the general technical development. The simpler physical properties like hardness and toughness, and how they are affected by the chemical composition and heat treatment of the steels, have been fairly well known. Already decades ago the conventional steels have empirically reached their optimum length of life. This is clearly shown in the publication "Test och utva/ rdering av slitage-motst.ang.ndet hos Va/ gst.ang.l" (Teknikum, Uppsala universitet, December 1983. ISSN 0346-8887).
The knowledge of tribology, i.e., the teaching of friction, lubrication and wearing, was however rather rudimentary outside the academic world. The manufacturers of the conventional road planing cutters had virtually no knowledge of tribology. Studies of the research results of recent years have however shown that the wearing mechanics when working road surfaces are no isolated functions but cooperate with each other under the influence of a number of other parameters. These studies have shown that the wearing of tool and pin is in micro scale. Fractures in and outside grain boundaries and wearing of tools takes place on surfaces that can be smaller than a square millimeter. This is documented in the publication "Tribological testing of traditional road-grading steel leading to the evolution of new road preparation concepts", (Wear 130, 1989, s. 151-165).
Systematic and methodical follow-up has occurred from 1984 and onwards and the use of the SYSTEM 2000.RTM. road-working equipment of Sandvik AB, a system solution for road planers in maintenance work that relies on SE-A-8404673-9, which corresponds to U.S. Pat. No. 4,784,517 which is hereby incorporated by reference in its entirety. However, these follow ups have now shown that cemented carbide tools in the market cannot solve all the frequent problems that arise in working road surfaces. This is partly due to the fact that the pins as a result of the working leave a roadway with grooves that may be troublesome and that too much material passes between the pins. Attempts to eliminate these inconveniences have previously been tried by placing the pins closer to each other by drilling the mounting holes in the mounting plate closer to each other. This change gave rise to mounting problems and problems with too low surface pressure to work the material underneath.
From SE-A-8404673-9 (the so-called conventional pins) is previously known a road planing cutter as mentioned above. The tools used in connection with the road planing cutter have been of standard design, i.e., the same type of tools that are used for asphalt milling, coal breaking etc. These tools are thus designed to carry out a cutting operation and therefore a common feature of them is that the cemented carbide insert has a relatively pointed design to minimize the cutting forces. In early use of these conventional pins, standard pins, it was found that relatively extensive damage of the road surfacing occurred already at a few degrees increase of the angle between the longitudinal axis of the pin and the horizontal plane. It was also found that the relatively small increase of the angle also caused a rolling working to transfer into a cutting non-rolling working. This type of cutting is negative due to the fact that the material in, e.g., a gravel roadway was cut down and thereby the stone material, which gives the roadway its bearing capacity, was cut down and segregated into smaller fractions with lower bearing capacity. Also the wear upon the tool itself was more than ten times greater than when the angle was absolutely correct. The relatively minor increase in the angle also causes a relatively low specific contact pressure between tool and the road surface to rapidly transfer into an extremely high surface pressure with extensive damage to the road surfacing as a consequence. The pointed standard pins (SE-A-8404673-9) have thus a very small scope of latitude before damages occur both in the road surfacing and in the tool itself.
A further development of SYSTEM 2000.RTM. through SE-B-8701222-5 (the so-called blunt pin), shows that a tool with a smoothly curved shape defining surface has a large scope of latitude whereby the angle that the longitudinal axis of the tool forms with the horizontal plane can be varied within relatively wide limits without affecting the function of the tool to any degree worth mentioning. The friction/pressure and degree of working of the tool are fairly equal within 20.degree.-90.degree. inclination between the longitudinal axis of the tool and the horizontal plane. Also the working continually takes place as a rolling crushing working whereby very long life for the tool is achieved. The smoothly curved shape defining surfaces of the tool also continually cause a significant reduction of the maximum specific surface pressure against the ground, whereby damages in the road surfacing can be avoided to a high extent.
In these studies one has been able to distinguish between the totally different ways of working and working results of the conventional pins way to work material and the dull pins way to work material. It has therefore been possible to systematically and 10 methodically determine the system structure and type of motion and type of wear of the pins in the marketplace. It has therefore been possible to consider advantages and drawbacks of the different types of pins and their stability and limitation as regards function.
A disadvantage and weakness of the above mentioned pin with the rounded shape defining surfaces, that cause the structural limitation of the maximum surface pressure, is that the pin due to its design is not able to penetrate hard/tough ice or hard/tough other material that cannot be worked by crushing.
The above described pins and other known cemented carbide pins have bodies with a concave or conical portion that closest to their mounting part has an essentially larger diameter than the rest of the tool body. This design with a thicker base diameter and an essentially thinner tip diameter has been functionally determined by the original areas of use for the conventional cemented carbide tools, i.e., milling, cutting, working. This geometrical shape of the holder body for the cemented carbide tip does not bring about an optimum function of the tool nor does it solve all the technical problems inherent in ground preparation.
The previously known pins that were designed with a concave portion could also contribute to a premature breakdown through fracture of the conical portion due to the smaller diameter of the initially weaker thinner portion.
Two essentially different ways to work material from solid bodies have been described above. The first way is a solid body performing a sliding, cutting abrasive wearing. The other way is a rolling body performing a crushing working.